Microbial Metabolism Questions and Answers

Q: Unlike active transport, passive and facilitated diffusion do not require

Correct answer: all of thesePassive and facilitated diffusion both move solute down its electrochemical gradient, so they need none of the three: no metabolic energy, and no ability to concentrate or accumulate solute against a gradient. Facilitated diffusion differs from simple diffusion only in using a carrier protein, which makes it faster and specific but no less passive. Doing any of these things is what defines active transport.

Q: Nitrogen fixation is a process that requires

Correct answer: both (a) and (b)Nitrogen fixation needs both. It is enormously expensive in energy - some 16 ATP per N2 reduced - because the triple bond is so strong. And nitrogenase is irreversibly inactivated by oxygen, so the reaction must take place in an anaerobic setting: a heterocyst, a root nodule protected by leghaemoglobin, or an anaerobic habitat.

Q: Bacteriochlorophyll differs from chlorophyll in what way?

Correct answer: Both (b) and (c)Bacteriochlorophyll and chlorophyll differ in their side groups and, as a direct consequence, in their absorption spectra - bacteriochlorophyll absorbs in the near infrared where chlorophyll cannot. What they share is the chelated metal: both hold magnesium at the centre of the ring, so the first statement is false.

Q: Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive sulphur. At the end of 48 hours, it is expected to find the radioactive label located in

Correct answer: enzymesSulfur enters the cell chiefly as cysteine and methionine, so a 35S label ends up in proteins, enzymes among them. Nucleic acids contain no sulfur at all, which is exactly what Hershey and Chase exploited when they used 35S to label phage protein and 32P to label its DNA.

Q: An organic nutrient essential to an organism’s metabolism that it cannot synthesise for itself is termed a/an:

Correct answer: growth factorA growth factor is an organic compound - a vitamin, an amino acid, a purine or pyrimidine - that an organism must have but cannot make for itself, so it has to be supplied in the medium. Trace elements and micronutrients are inorganic and needed only in minute amounts.

Q: The source of the necessary elements of life is:

Correct answer: an inorganic environmental reservoirEvery element in a living thing comes ultimately from an inorganic reservoir - the atmosphere, the oceans, the rocks and soil - and returns to it. The sun supplies energy, not matter, which is why energy flows through an ecosystem while elements cycle round it.

Q: An organism that can synthesize all its required organic components from CO2 using energy from the sun is a:

Correct answer: photoautotrophThe name states both halves: photo- for light as the energy source, autotroph for CO2 as the carbon source. Plants, algae and cyanobacteria are photoautotrophs. A photoheterotroph uses light but needs organic carbon; a chemoautotroph fixes CO2 using energy from inorganic chemical oxidations.

Q: An obligate halophile requires high:

Correct answer: saltHalophile means salt-loving, and an obligate one cannot grow without a high salt concentration - the extreme haloarchaea require several molar NaCl and lyse in fresh water. Their cytoplasm is kept osmotically balanced by accumulating potassium ions or compatible solutes.

Q: Chemoautotrophs can survive on ______alone.

Correct answer: minerals and CO2A chemoautotroph takes its energy from oxidising an inorganic compound such as ammonia, nitrite, sulfide or ferrous iron, and its carbon from CO2. So it needs minerals and CO2 and nothing organic at all - which is what lets such organisms colonise bare rock and deep-sea vents.

Q: Which of the following statements is true for all organisms?

Correct answer: they require inorganic nutrientsEvery organism needs inorganic nutrients - water, and sources of nitrogen, phosphorus, sulfur, potassium and the trace metals. The other three are not universal: autotrophs need no organic carbon, many organisms make all their own growth factors, and anaerobes are poisoned by oxygen.

61.

Unlike active transport, passive and facilitated diffusion do not require

A.metabolic energy
B.concentration of solute against an electrochemical gradient
C.accumulation of solute against an electrochemical gradient
D.all of these

Answer: A

Correct answer: all of these

Passive and facilitated diffusion both move solute down its electrochemical gradient, so they need none of the three: no metabolic energy, and no ability to concentrate or accumulate solute against a gradient. Facilitated diffusion differs from simple diffusion only in using a carrier protein, which makes it faster and specific but no less passive. Doing any of these things is what defines active transport.

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62.

Nitrogen fixation is a process that requires

A.energy
B.an anaerobic environment
C.both (a) and (b)
D.an aerobic environment

Answer: C

Correct answer: both (a) and (b)

Nitrogen fixation needs both. It is enormously expensive in energy - some 16 ATP per N₂ reduced - because the triple bond is so strong. And nitrogenase is irreversibly inactivated by oxygen, so the reaction must take place in an anaerobic setting: a heterocyst, a root nodule protected by leghaemoglobin, or an anaerobic habitat.

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63.

Bacteriochlorophyll differs from chlorophyll in what way?

A.The chelated metal in bacteriochlorophyll is not Mg
B.There are chemical differences between the two chlorophyll in their side (R) groups
C.They have different absorption spectra
D.Both (b) and (c)

Answer: D

Correct answer: Both (b) and (c)

Bacteriochlorophyll and chlorophyll differ in their side groups and, as a direct consequence, in their absorption spectra - bacteriochlorophyll absorbs in the near infrared where chlorophyll cannot. What they share is the chelated metal: both hold magnesium at the centre of the ring, so the first statement is false.

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64.

Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive sulphur. At the end of 48 hours, it is expected to find the radioactive label located in

A.DNA
B.enzymes
C.RNA
D.all of these

Answer: B

Correct answer: enzymes

Sulfur enters the cell chiefly as cysteine and methionine, so a ³⁵S label ends up in proteins, enzymes among them. Nucleic acids contain no sulfur at all, which is exactly what Hershey and Chase exploited when they used ³⁵S to label phage protein and ³²P to label its DNA.

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65.

An organic nutrient essential to an organism’s metabolism that it cannot synthesise for itself is termed a/an:

A.trace element
B.micronutrient
C.growth factor
D.essential nutrient

Answer: C

Correct answer: growth factor

A growth factor is an organic compound - a vitamin, an amino acid, a purine or pyrimidine - that an organism must have but cannot make for itself, so it has to be supplied in the medium. Trace elements and micronutrients are inorganic and needed only in minute amounts.

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66.

The source of the necessary elements of life is:

A.an inorganic environmental reservoir
B.the sun
C.rocks
D.the air

Answer: A

Correct answer: an inorganic environmental reservoir

Every element in a living thing comes ultimately from an inorganic reservoir - the atmosphere, the oceans, the rocks and soil - and returns to it. The sun supplies energy, not matter, which is why energy flows through an ecosystem while elements cycle round it.

Discuss in Forum

67.

An organism that can synthesize all its required organic components from CO2 using energy from the sun is a:

A.photoautotroph
B.photoheterotroph
C.chemoautotroph
D.chemoheterotroph

Answer: A

Correct answer: photoautotroph

The name states both halves: photo- for light as the energy source, autotroph for CO₂ as the carbon source. Plants, algae and cyanobacteria are photoautotrophs. A photoheterotroph uses light but needs organic carbon; a chemoautotroph fixes CO₂ using energy from inorganic chemical oxidations.

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68.

An obligate halophile requires high:

A.pH
B.temperature
C.salt
D.pressure

Answer: C

Correct answer: salt

Halophile means salt-loving, and an obligate one cannot grow without a high salt concentration - the extreme haloarchaea require several molar NaCl and lyse in fresh water. Their cytoplasm is kept osmotically balanced by accumulating potassium ions or compatible solutes.

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69.

Chemoautotrophs can survive on ______alone.

A.minerals
B.CO2
C.minerals and CO2
D.methane

Answer: C

Correct answer: minerals and CO2

A chemoautotroph takes its energy from oxidising an inorganic compound such as ammonia, nitrite, sulfide or ferrous iron, and its carbon from CO₂. So it needs minerals and CO₂ and nothing organic at all - which is what lets such organisms colonise bare rock and deep-sea vents.

Discuss in Forum

70.

Which of the following statements is true for all organisms?

A.they require organic nutrients
B.they require inorganic nutrients
C.they require growth factors
D.they require oxygen gas

Answer: B

Correct answer: they require inorganic nutrients

Every organism needs inorganic nutrients - water, and sources of nitrogen, phosphorus, sulfur, potassium and the trace metals. The other three are not universal: autotrophs need no organic carbon, many organisms make all their own growth factors, and anaerobes are poisoned by oxygen.

Discuss in Forum

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